A current mode control is known as one of control methods of a chopper switching regulator. In the current mode control, a detection result of a reactor current is incorporated in a feedback loop that controls a switching time based on an error signal indicating error of a measured value with respect to a command value of an output voltage. Accordingly, the reactor current is controlled in accordance with change in output voltage.
In a case where a load current drastically changes, until the control follows the change, electric charge is supplied from a smoothing capacitor connected between output terminals to which a load is connected. Because change in an output voltage (i.e., a voltage between both ends of a capacitor) and change in the error signal appear later than change in the load current, a response of the control delays, and the output voltage is temporarily reduced due to the delay of the response.
JP-A-2002-281742 (corresponding to US 2002/0135345 A1) discloses a control method in which a difference between the reactor current and the load current is incorporated in the feedback loop. In a buck circuit, the difference between the reactor current and the load current corresponds to a change component of the load current. Thus, the control can directly respond to the change in the load current and can reflect the change in the load current on the reactor current.
However, a device disclosed in JP-A-2002-281742 can be applied only to a switching regulator (e.g., a buck switching regulator) in which a reactor current corresponds with an output current in a steady operation state.
In a boost switching regulator, a reactor current does not correspond with an output current even in a steady operation state. Thus, the device cannot detect change in the load current with accuracy and cannot improve a response to the load current sufficiently.